1. Field of the Invention
The present invention relates to a light emitting diode, and more particularly, to a light emitting diode having an AlInGaP active layer and a method of fabricating the same.
2. Discussion of the Background
A light emitting diode (LED), which is a photoelectric conversion semiconductor device having a structure in which an n-type semiconductor of which majority carriers are electrons and a p-type semiconductor of which majority carriers are holes are joined together, emits light through recombination of these electrons and holes. In particular, an AlInGaP compound semiconductor has been applied to a high-quality semiconductor laser for emitting light with a wavelength of about 670 nm. Further, the AlInGaP compound semiconductor has been applied to an LED for emitting light in a wavelength range of 560 to 680 nm by adjusting a ratio of Al and Ga.
FIG. 1 is a sectional view of a conventional LED having an AlInGaP active layer.
Referring to FIG. 1, an N-type AlInGaP lower semiconductor layer 11 is grown on an N-type GaAs substrate 10, and an AlInGaP active layer 12 is grown on the N-type AlInGaP lower semiconductor layer 11. Subsequently, a P-type AlInGaP upper semiconductor layer 13 is grown on the AlInGaP active layer 12. These semiconductor layers may be grown through various methods, e.g., methods including a metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). Then, an electrode 14 is formed on the upper semiconductor layer 13, and an electrode 15 is formed on a rear surface of the substrate 10.
The lower and upper semiconductor layers 11 and 13, which are confining layers for helping electrons and holes to be recombined in the active layer 12, are formed of a material having a larger bandgap as compared with the active layer 12.
Since the LED is fabricated by growing AlInGaP epitaxial layers on a conductive substrate, the electrode 15 is formed on the rear surface of the substrate to thereby drive the LED.
Meanwhile, since the electrode 14 is formed on the upper semiconductor layer 13 of which the specific resistivity is high, the LED has a problem of current distribution. To solve such a problem, technologies for employing a transparent window layer with low specific resistivity have been disclosed in U.S. Pat. Nos. 5,008,718 and 5,233,204. According to the documents, a window layer with low specific resistivity, e.g., a GaAsP, AlGaAs or GaP layer, is grown on the upper semiconductor layer 13 for the purpose of uniform current distribution, thereby improving the light emitting efficiency.
Further, in U.S. Pat. Nos. 5,376,580 and 5,502,316, after growing AlInGaP epitaxial layers on a light absorptive substrate such as a GaAs substrate, the substrate is separated from the epitaxial layers, and the epitaxial layers are bonded to a light transmissive substrate such as GaP, thereby improving the light emitting efficiency.
However, since an LED emits light by a forward current, the conventional LED is repeatedly turned on/off depending on current directions when the conventional LED is connected to an AC power source and is then operated. Hence, additional components such as a converter for converting AC into DC are required in order to use the conventional LED by being directly connected to the AC power source. Such additional components make it difficult to substitute an LED for a conventional fluorescent lamp due to their incidental expenses.